TEX-ELZ triple insulated wire

enamel to enamel has no rating whatsoever - where are you ? China ? India ? Bangladesh ?

The authors aren't obligated to do any such thing, especially if they make it clear that they are making a recommendation, rather than a requirement.

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The product is from my friend who is in India, but i am not sure if its in wide sale there. So, if enamel to enamel wound SMPS has no isolation rating, then its pointless using a 6mm gap between primary and secondary of the offline flyback SMPS?

you are confused - enamel to enamel, pri to sec is a no go - as for safety and standards considerations the enamel is not there - as it can be nicked and abraded during manufacture

for a pri or sec wdg where the volts per turn are low - the enamel serves a useful purpose as working voltage insulation - if it fails there will be a shorted turn protected by either a fuse or by some current limiting device.

If pri to sec fails - you only find out when some one touches it - oops - too late.

Proper TIW wire meets the safety regs on a transformer - provided it doesn't get too hot and provided the lead out wires do not get too close ( often fixed by proper sleeving ).

However a layer of Kapton or other is a very good idea with TIW pri and enamel sec - you should always design a supply such that if your Grandmother was on life support in hospital and your power supply was providing power to human connected instruments - you could easily sleep at night knowing a 4kV mains spike would not compromise the insulation and allow 230Vac to your Granny.

thanks, and the 4kv isol test is all about "if it can withstand 4kv for one minute, then it can withstand normal mains on pri, and earthed sec, for x years"?

ie, the "4kv isol test" is nothing to do with being able to handle 4kv mains transients?....for mains transient testing, we have different tests which literally fire transients into the smps input.

in sumary "4kv for one mintue", is all about how good the insulation is for use in normal mains with no transients....ie will it break down over time (even if there were no mains transients)?